1. Field of the Invention
This invention relates generally to pipe connections and more particularly to an improved method and apparatus for forming a quick-coupling connecting nipple for plastic pipe.
2. Description of the Prior Art
The use of plastic pipe has gained growing acceptance in many industries over steel pipe because of its favorable features. Illustrative, but not exhaustive, of some applications are oilfield and open mine pit pumping, underground air and water piping, temporary piping and dredge piping. Plastic pipe is seventy percent lighter than steel and is therefore preferable for handling and installation. Plastic pipe has also proved to be abrasion-proof and corrosion-resistant in a chemical environment. Also, plastic pipe can withstand extreme temperature flexing and cold bending thereby making it more attractive for use over steel pipe. Two particular types of plastic pipe widely used are polyethylene pipe and polypropylene pipe.
Because of the advantageous features of plastic pipe which demand that it be used in long lengths, it has become necessary to develop a means to quick-couple lengths of the pipe. Because of the inherent material characteristics of ductility and elasticity of polypropylene and polyethylene pipe, a rigid sleeve is required in the coupling. Current coupling techniques use a steel sleeve secured on the end of the plastic pipe. An example of the prior art is the "POLYGROOVE".TM. polyethylene pipe and connection manufactured by Pipe Systems, Inc. of St. Louis, Mo. The POLYGROOVE.TM. connection includes a steel sleeve with two annular rolled grooves provided thereon which is glued to the end of the plastic pipe.
The edge of the sleeve presents an annular shoulder outwardly from the nominal diameter of the pipe. Such a shoulder presents a disadvantage in the art of connecting plastic pipe because it may be exposed to snagging thereby precipitating loosing or removal of the steel sleeve from the plastic pipe in handling and installation. This loosening presents opportunities for passages to be formed between the sleeve and the pipe allowing effluent and influent leakage of fluids. It is obvious that leaky pipe connections would make the use of plastic undesirable. Therefore, an improved low cost method and apparatus for forming nipple connections with a rigid sleeve secured to the ductile and elastic pipe has been required.
It is, therefore, an object of the present invention to provide an improved method and apparatus for effectively and efficiently forming a connecting nipple for a quick-coupling plastic pipe connection which is not subject to the disadvantages discussed above.
More specifically, it is an object of this invention to provide an improved method and apparatus as aforesaid wherein a metal sleeve is secured to plastic pipe by a friction fit.
Another object of this invention is to provide an improved method and apparatus as aforesaid where the end of the metal sleeve is crimped onto the plastic pipe thereby eliminating a shoulder on the sleeve.
Still another object of this invention is to provide an improved method and apparatus as aforesaid which eliminates leaking of the nipple through passages between the sleeve and said pipe and by crimping the outer surface of the sleeve flush to the outer surface of the plastic pipe.
Yet another object of the invention is to provide an improved method and apparatus as aforesaid which allows the use of the quick-coupling connection with polyethylene or polypropylene pipe that can withstand high fluid pressures.